Moving-picture signal coding and/or decoding system resistant to transmission error

ABSTRACT

An input image signal is coded by an encoder to be outputted as a basic code string, and the basic code string is delayed by a code-string delay circuit for a predetermined period of time to be outputted as an additional code string. The basic code string is synthesized with the additional code string by a code-string synthesizer to be outputted as an output code string. Thus, there is provided an image data coding system which can quickly restore data even if the data is lost due to error and in which the increased code amount is less than the cycle refresh and the error correction.

More than one reissue application has been filed for the reissue of U.S.Pat. No. 6,701,018. The currently pending reissue applications areapplications Ser. Nos. 11/366,010; 12/232,511; 12/654,141; 12/762,604;12/762,642; 12/762,669; 12/232,509; 12/654,140; 12/763,064; 12/763,052;12/763,036; 12/762,722; 12/272,510; 12/591,980; 12/762,864; 12/762,834;12/762,793; 12/762,756; 12/762,686; 12/272,508; 12/591,981; 12/762,795;12/762,972; 12/762,983; 12/762,745; 12/762,998; and 12/762,935.

This is a divisional reissue application of U.S. reissue applicationSer. No. 12/591,980, filed Dec. 7, 2009, which is a divisional reissueapplication of U.S. reissue application Ser. No. 12/232,510, filed Sep.18, 2008, which is a divisional reissue application of U.S. reissueapplication Ser. No. 11/366,010, filed Mar. 2, 2006, now abandoned,which is a reissue application of U.S. Pat. No. 6,701,018, which is adivisional of application Ser. No. 09/471,415 filed Dec. 23, 1999, nowU.S. Pat. No. 6,408,098, which is a continuation application ofapplication Ser. No. 09/306,983, filed May 7, 1999, now U.S. Pat. No.6,035,069 issued Mar. 7, 2000, which is a divisional of application Ser.No. 08/738,171, filed Oct. 25, 1996, now U.S. Pat. No. 5,930,395 issuedJul. 27, 1999, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an image data coding and/or decodingsystem for compressing and coding an image data into a smaller amount ofdata and for decoding code strings obtained by the compression coding toreproduce an image. More specifically, the invention relates to an imagedata coding and/or decoding system which has high error resilience andwhich can transmit and/or store a coded image data of high quality evenif the coded image data is transmitted and/or stored via a mediumwherein an error easily occurs, such as a radio channel.

In an image transmitting and/or storing system such as a videotelephone, a videoconferencing system, a portable information terminal,a digital video disc system and a television broadcasting system,various systems, which include the motion compensation, the discretecosine transform, the sub-band coding, the pyramid coding and thecombinations thereof, have been developed as techniques for compressingand coding an image data into a smaller amount of data fortransmission/storing. In addition, as international standard methods forcompressing and coding a moving picture, the methods “ISO•MPEG1”,“ISO•MPEG2”, “ITU-T•H.261”, and “ITU-T•H.262” are standardized. Allthese methods are compressing and coding methods, each comprising acombination of the motion-compensated adaptive prediction and thediscrete cosine transform, and described in detail in “InternationalStandard of Multimedia Coding” (edited and written by Hiroshi Yasuda,published by Maruzen, June 1991) (Literature 1) and so forth.

As an example of conventional moving-picture coding systems, the basicconstruction of a coding system using the motion-compensated adaptiveprediction and the discrete cosine transform is shown in FIG. 1. In thisfigure, after an input image signal S1 is divided into a plurality ofregions defined by a region divider 1, the motion-compensated adaptiveprediction is carried out. That is, a motion-compensated adaptivepredictor 2 detects a motion vector between the input image signal S1and a reference image signal S2 of the previous frame, which is storedin a frame memory 3 and which has been already coded and locallydecoded, and performs the motion compensation with respect to thereference image signal using the detected motion vector, so as toproduce a prediction signal. However, in the motion-compensated adaptivepredictor 2, a preferred prediction mode is selected from intraframecodings (prediction signal=0) directly using the motion compensatedprediction and the input image signal S1, and the prediction signal S3corresponding to the prediction mode is outputted.

Then, in a subtracter 4, the prediction signal S3 is subtracted from theinput image signal S1 to output a predictive residual signal S4. Withrespect to each of blocks of a predetermined size, the discrete cosinetransform (DCT) of the predictive residual signal S4 is carried out bymeans of a discrete cosine transformer 5. The DCT coefficient obtainedby the discrete cosine transform is quantized by means of a quantizer 6.The DCT coefficient quantized by the quantizer 6 is divided into twoportions. One of the two portions is coded by means of a variable-lengthencoder 7, and then, it is multiplexed with the motion vector, which hasbeen coded by a variable-length encoder 9, by means of a multiplexer 8to be outputted as a bit-stream. The other portion is inverse-quantizedby means of a inverse quantizer 10, and then, the inversediscrete-cosine transform (inverse DCT) thereof is carried out by meansof an inverse discrete-cosine transformer 11. The output of the inversediscrete-cosine transformer 11 is added to the adaptive predictionsignal S3 by means of an adder 12 to be a locally decoded signal to bestored in the frame memory 3.

FIG. 2 is a view illustrating the basic construction of a moving-picturedecoding system which corresponds to the moving-picture coding system ofFIG. 1. The code string transmitted from the moving-picture codingsystem to be stored is divided into a quantized DCT coefficient and amotion vector data by means of a demultiplexer 13. The quantized DCTcoefficient data passes through a variable-length decoder 14, a inversequantizer 15 and a inverse discrete-cosine transformer 16, to beoutputted as a predicted error signal S6. The motion vector data isdecoded by means of a variable-length decoder 17, and then, it isinputted to a motion-compensation predictor 18. In themotion-compensation predictor 18, the motion compensation to a referenceimage signal S7 of the last frame in a frame memory 19 is carried outusing the motion vector to produce a prediction signal S8. Then, in anadder 20, the predicted error signal S6 is added to the predictionsignal S8 to reproduce an image signal S9. The reproduced image signalS9 is outputted to the outside of the system and stored in the framememory 19 as the reference image signal S7.

However, in such a conventional moving-picture coding and/or decodingsystem, there are the following problems.

In a channel in which an error may be mixed, such as a radio channel,when only the aforementioned coding is carried out, the quality of thedecoded image is remarkably deteriorated if an error occurs. Inparticular, when there is an error in a signal such as a synchronizingsignal, a mode data and a motion vector, the picture quality isremarkably deteriorated.

In addition, as mentioned above, the motion-compensated adaptiveprediction coding is frequently used in the moving picture coding.However, since only the interframe difference is coded in themotion-compensated adaptive prediction coding, when an error occurs, theframe is not only incorrect, but an incorrect image is also stored in aframe memory, so that a predicted image is prepared using the incorrectimage and a residual error is added thereto. For that reason, even ifthe subsequent frame is correctly decoded, it is not possible to obtaina correctly decoded image in the subsequent frame, except that when thedata is transmitted in a mode (INTRA mode) wherein the coding isperformed in only the frame without using the interframe difference orwhen the influence of the error is gradually attenuated to return to theoriginal state.

FIG. 3 illustrates this condition. This example shows the condition thata black circle is moving. Signals including a residual signalrepresentative of a circle of the next frame (expressed by the blackcircle of the residual signal) and a residual signal for erasing acircle of the last frame (expressed by a dotted-line circle of theresidual signal) are outputted as interframe differential is signals. Inthis case, the motion compensation is not performed for simplification,and the interframe difference is obtained assuming that MV (motionvector)=0.

If data of one frame is lost due to error, the second frame is notdecoded at all, and for example, the first frame is outputted as it is.In the third frame, a residual error, which is capable of correctlydecoding if it is added to the second frame, is added to the first frameto reproduce a quite different image. Thereafter, since the residualerror is added to the incorrect image, the error is not basicallyerased, so that it is not possible to reproduce a correctly decodedimage.

In order to eliminate the aforementioned problem, a method called“refresh” for coding in the INTRA mode every a predetermined cycle hasbeen conventionally used. In this case, when the coding is performed inthe INTRA mode, the code amount is increased to remarkably deterioratethe picture quality when no error occurs. Therefore, methods such as thecyclic refresh for refreshing every few macroblocks in one frame, notsimultaneously refreshing the whole picture, are generally used.However, although the cyclic refresh is able to resstring the increaseof the code string, there is a problem in that it takes a long timeuntil the normal state is restored.

As other measures against errors; there is the use of the errorcorrection coding. The error correction coding is able to correct errorscaused at random. However, if errors of hundreds bits occur at a burstand continuously, it is difficult to correct such errors. Even if it ispossible to correct such errors, a very long redundancy is required.

As mentioned above, in en image coding, particularly in a moving-picturecoding, the loss of data due to error greatly deteriorates the picturequality. In addition, in the conventional methods such as the cyclicrefresh for restoring the lost data due to error, there are problems inthat it takes a long time until it is restored considering the codingefficiency, and that the attempt to decrease the time required torestore the lost data increases the code amount to lower the efficiency.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amoving-picture coding and/or decoding system which can quickly restoreif data is lost due to error and in which the increased code amount isless than those of the refresh and the error correction.

In order to accomplish the aforementioned and other objects, accordingto one aspect of the present invention, a moving-picture decoding systemcomprises: coding means for coding an input image signal to output abasic code string; code-string delay means for delaying the basic codestring for a predetermined period of time to output as an additionalcode string; and code-string combining means for combining the basiccode string with the additional code string to output the synthesizedcode string.

According to another aspect of the present invention, a moving-picturedecoding system corresponding to the aforementioned moving-picturecoding system, comprises: code-string dividing means for dividing aninput code string into a basic code string and an additional code stringobtained by delaying the basic code string; decoding means for decodingthe basic code string or the additional code string to output a decodeddata; error discriminating means for discriminating whether it ispossible to decode the basic code string from the decoded data by thedecoding means; and code-string switching means for inputting the basiccode string to the decoding means when it is discriminated by thediscriminating means that it is possible to decode the basic code stringby the decoding means, and for inputting the additional code string tothe decoding means when it is discriminated by the discriminating meansthat it is impossible to decode the basic code string by the decodingmeans.

Thus, according to the present invention, after the code string obtainedby coding the input image signal is outputted as the basic code string,the additional code string which is basically the same as the basic codestring is outputted again after a predetermined period of time.Therefore, even if the first outputted data of the basic code string isdestroyed due to error during the transmission/storing, it iscompensated by the data of the additional outputted after apredetermined period of time, so that the decoding is correctlyperformed.

In addition, according to the present invention, an additional codestring simplified by selecting only important data and so forth may beoutputted to reduce the code amount, in place of the directly outputtingof the same additional code string as the first outputted basic codestring. The image data decoding system includes interpolating means forinterpolating the parts of the additional code string simplified toreduce the code amount, and decodes the additional code string after theinterpolation when it is discriminated that it is impossible to decodethe basic code string. Thus, it is possible to improve the errorresilience without remarkably deteriorating the decoded image when noerror occurs.

Moreover, according to the present invention, a synchronizing signal maybe added to the additional code string in the moving-picture codingsystem so as to form one frame by only the additional code string. Inthis case, the moving-picture decoding system discriminates the basiccode string from the additional code string by the synchronizing signaladded to the additional code string, and divides the input code stringinto the basic code string and the additional code string on the basisof the discriminated results. This, since the moving-picture decodingsystem can discriminate the basic code string from the additional codestring by only detecting the synchronizing signal, its construction issimple. In addition, if the synchronizing signal is thus added to theadditional code string, the total number of the synchronizing signalsincreases, so that the opportunity for restoring the synchronismincreases.

As mentioned above, according to the present invention, it is possibleto provide a moving-picture coding and/or decoding system, which canquickly restore if data is lost due to error caused during thetransmission/storing, in which the deterioration of quality of thedecoded image is small, in which the increase of the code amount issmaller than those in the cyclic refresh and the error correction whichhave been conventionally performed as the measures against errors, andwhich has a high coding efficiency.

That is, according to the present invention, after a code stringproduced by coding an input image signal is outputted as a basic codestring, an additional code string having basically the same contents isoutputted again after a predetermined period of time, so that it ispossible to perform the correct decoding using the data of theadditional code string even if the data of the basic code string isdestroyed due to errors caused during the transmission/storing.

In addition, if an additional code string simplified by selecting onlyimportant data from the basic code string and so forth to reduce thecode amount, is outputted as the additional code string to interpolatethe simplified parts of the additional code string on the decoding sidefor decoding, it is possible to further improve the error resiliencewithout remarkably deteriorating the quality of the decoded image whenno error occurs.

Moreover, a synchronizing signal may be added to the additional codestring to form one frame by only the additional code string, so that thebasic code string may be discriminated from the additional code stringby the synchronizing signal added to the additional code string on thedecoding side so as to divide the input code string into the basic codestring and the additional code string. Thus, the construction is simpleand the total number of the synchronizing signals increases, so that theopportunity for restoring the synchronism. Therefore, it is possible tofurther improve the error resilience.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of a conventional moving-picture codingsystem;

FIG. 2 is a block diagram of a conventional moving-picture decodingsystem;

FIG. 3 is a view illustrating the influence of an error in theconventional system:

FIG. 4 is a block diagram of the first preferred embodiment of amoving-picture coding system according to the present invention;

FIG. 5 is a view illustrating a construction of code strings in thefirst preferred embodiment;

FIG. 6 is a block diagram of the first preferred embodiment of amoving-picture decoding system according to the present invention;

FIG. 7 is a block diagram of the second preferred embodiment of amoving-picture coding system according to the present invention;

FIG. 8 is a view illustrating a construction of code strings in thesecond preferred embodiment;

FIG. 9 is a view illustrating an example of a method for selecting aband of a predictive residual signal in the second preferred embodiment;

FIG. 10 is a block diagram of the second preferred embodiment of amoving-picture decoding system according to the present invention;

FIG. 11 is a block diagram of the third preferred embodiment of amoving-picture coding system according to the present invention;

FIG. 12 is a view illustrating a construction of code strings in thethird preferred embodiment;

FIG. 13 is a block diagram of the third preferred embodiment of amoving-picture decoding system according to the present invention;

FIG. 14 is a view illustrating another construction of code strings inthe third preferred embodiment;

FIG. 15 is a view illustrating a decoding method when an error occurs inthe third preferred embodiment;

FIG. 16 is a view illustrating a decoding method when an error occurs inthe third preferred embodiment;

FIG. 17 is a view illustrating a decoding method when an error occurs inthe third preferred embodiment;

FIG. 18 is a block diagram of the fourth preferred embodiment of acode-string simplifier according to the present invention;

FIG. 19 is a block diagram of the fifth preferred embodiment of an imagedata decoding system according to the present invention;

FIG. 20 is a block diagram of the sixth preferred embodiment of an imagedata decoding system according to the present invention;

FIG. 21 is a view illustrating an example of a construction of a codestring for the explanation of the seventh preferred embodiment of thepresent invention;

FIG. 22 is a view illustrating an example of operation when acode-string discriminator is malfunctioned for the explanation of theseventh preferred embodiment;

FIG. 23 is a flow chart illustrating an algorithm in a code-stringdiscriminator in the seventh preferred embodiment;

FIG. 24 is a view illustrating an example of discrimination of a basiccode string corresponding to an additional code string in the seventhpreferred embodiment;

FIG. 25 is a flow chart illustrating an algorithm in a code-stringdiscriminator in the seventh preferred embodiment, which considers anerror in the code-string discriminator;

FIG. 26 is a view illustrating an example of a discriminating method inthe seventh preferred embodiment, which considers an error;

FIG. 27 is a view illustrating a decoded-value selecting method in adecoded-value selector in the eight preferred embodiment of the presentinvention;

FIG. 28 is an example of a decoded-value selecting method performed inview of an error which has not found when decoding, in the eightpreferred embodiment;

FIG. 29 is a .block diagram of a simplification control section in theninth preferred embodiment of an image data coding system according tothe present invention;

FIG. 30 is a block diagram of an example of a system to which thepresent invention is applied; and

FIG. 31 is a block diagram schematically illustrating a moving-picturecoding system and a moving-picture decoding system which are used in thesystem of FIG. 30.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, the preferred embodiments of the presentinvention will be described below.

FIG. 4 is a block diagram of the first preferred embodiment of amoving-picture coding system according to the present invention. Aninput image signal S10 is coded in an encoder 21 to be outputted as acode string (which will be hereinafter referred to as a “basic codestring”). The basic code string S11 is directly inputted to acode-string synthesizer 23. The basic code string S11 is also inputtedto a code-string delay circuit 22 wherein it is stored and retained fora predetermined period of time, and then it is outputted.

That is, the code-string delay circuit 22 outputs the retained past codestring (which will be hereinafter referred to as an “additional codestring”) S12 after the predetermined period of time. This additionalcode string S12 is also inputted to the code-string synthesizer 23. Inthe code-string synthesizer 23, the basic code string S11 outputted fromthe encoder 21 is synthesized with the additional code string S12outputted from the code-string delay circuit 22, to be outputted as anoutput code string S13.

FIG. 5 is a view illustrating the constructions of an output code string(a) in a conventional system and output code strings (b) and (c) in thepreferred embodiment of the present invention. Although there arevarious methods for combining code strings in the code-stringsynthesizer 23, two types of methods are shown herein as examples.Furthermore, the PSC (Picture Synchronization Code) denotes asynchronizing signal in the figure.

The first proposed method shown in FIG. 5 is a method whereinimmediately after the basic code string S11 outputted without passingthrough the code-string delay circuit 22, the additional code stringS12, which is outputted from the code-string delay circuit 22 and whichis the same as the basic code string S1, is outputted again. In thisfirst proposed method, one frame includes two data of the same codestring. Therefore, even if an error occurs in one of the code stringdata, it is possible to correctly code on the decoding side by using theother code string data.

However, if a variable-length code is used in the code string, once anerror occurs, the pause between codes can not be found out, so that thestep-out which can not correctly decode may occur. Therefore, if thefirst proposed method is used in a system utilizing a variable-lengthcode, when an error occurs in the head basic code string, the subsequentadditional code string can not be correctly decoded. Accordingly, thismethod can be effectively used in a system using a fixed-length code orwhen the construction of code string which can be decoded in the inversedirection is used.

In addition, since the two same code strings are arranged, therespective code strings can be divided by deriving the bit number in onesynchronizing interval (from a synchronizing signal to the adjacentsynchronizing signal) to divide it into two equal parts. However, it isrequired to take notice that when the synchronizing signal is lost orwhen a false synchronizing signal occurs, the code amount in a correctsynchronizing interval can not be derived so as to cause malfunction.

The second proposed method shown in FIG. 5(c) is a method which can beutilized even if a usual variable-length code is used. In this method, acode string obtained by coding the frame of number n in the input imagesignal is used as a basic code string, and a code string obtained bycoding the frame of number n−1 in the input image signal is used as anadditional code string, so that these code strings are synthesized inone frame. Unlike the aforementioned first proposed method; in thismethod, the code string obtained by coding the frame of number n isoutputted again as the additional code string in the synchronizinginterval of number n+1. Therefore, even if the data wherein an erroroccurs is lost in the synchronizing interval of number n, the same dataexists in the next synchronizing interval of number n+1, so that it canbe used to correctly decode.

In this second proposed method, the second code string is synthesized inthe next synchronizing interval. Therefore, even if an error occurs,there is no influence of the error unless the next synchronizing signalis destroyed, so that it is not particularly required to consider theproblem with respect to the step-out of the variable-length code, suchas the problem caused in the first proposed method. However, when anerror occurs, the decoding can not correctly performed unless the signalin the next synchronizing interval is decoded. Therefore, in somemethods for constructing a decoder, the timing for outputting thedecoded image signal may be delayed in comparison with the originaltiming.

The first preferred embodiment of an image data decoding systemaccording to the present invention will be described below.

FIG. 6 is a block diagram of the first preferred embodiment of an imagedata decoding system according to the present invention, whichcorresponds to the image data coding system shown in FIG. 4. An inputcode string S13, which is outputted from the image data coding system ofFIG. 4 and which is inputted via a transmitting system or a storingsystem (not shown), is divided into a basic code string S11 and anadditional code string S12 by means of an additional code-string divider24. Typically, the basic code string S11 is selected by a switch 25 tobe inputted to a decoder 26.

The decoder 26 decodes the basic code string S11 and outputs adecoded-state indicative signal S14, which is representative of thedecoded state of the basic code string S11, to an error detector 27. Theerror detector 27 determines whether there is no error in the input codestring S13 and the decoded results of the decoder 26 on the basis of thedecoded-state indicative signal S14, and outputs an error detectionsignal S15, which is representative of the presence of error, to thedecoder 26. When the error detection signal S15 indicates that there isno error, the decoder 26 outputs the decoded results of the basic codestring as a decoded image signal S16, and when it indicates that thereis an error, the decoder 26 does not output the decoded results.

In addition, the error detector 27 outputs a switch control signal S17to the switch 25 so that when there is an error, the switch 25 ischanged over to select the additional code string S12 so as to input theadditional code string 512 to the decoder 26. In this case, the decoder26 decodes the additional code string S12, and when the error detector27 detects no error, the detector 26 outputs the decoded results thereofas the decoded image signal S16 in place of the decoded results of thebasic code string S11.

Furthermore, when there are errors in both of the basic code string S11and the additional code string S12, the decoder 26 may directly outputthe last frame.

Another preferred embodiment of the present invention will be describedbelow. Furthermore, in this preferred embodiment and other preferredembodiments after this preferred embodiment, the blocks defined by thesame names as those in FIGS. 4 and 6, which disclose the first preferredembodiment, have the same functions as those in the first preferredembodiment.

FIG. 7 is a block diagram of the second preferred embodiment of an imagedata coding system according to the present invention. This system isthe same as that in the first preferred embodiment, except that an inputimage signal S10 is coded by means of an encoder 21, and the resultingbasic code string S11 is transformed into a simplified code string S18in order to reduce the code amount thereof, and then, the simplifiedcode string S18 is inputted to a code-string delay circuit 22. Thesimplified code string S18 is delayed for a predetermined period of timeby means of the code-string delay circuit 22 to be outputted as anadditional code string S12. The additional code string S12 issynthesized with the basic code string S11 to be outputted as an outputcode string S13.

A code-string simplifier 28 is provided for reducing the code amount ofthe additional code string S12. Therefore, although the code-stringsimplifier 28 is arranged upstream of the code-string delay circuit 22in FIG. 7, it may be arranged downstream of the code-string delaycircuit 22.

According to this preferred embodiment, since the code amount of theadditional code string S12 is less than that of the basic code stringS11, it is possible to realize the same amount of error resilience asthat in the first preferred embodiment, by a smaller increase of codeamount than those in conventional methods. In addition, since theincrease of the code amount is small, when there is a smaller error thanthat in the first preferred embodiment, it is possible to obtain adecoded image of better quality.

On the other hand, if the basic code string S11 is destroyed when anerror occurs and if the decoding is performed by the additional codestring S12, the decoded results may remain having distortion to someextent since the additional code string is simplified to reduce theamount of data. However, if the method for simplifying the code stringis devised, it is possible to decrease the distortion so that there isvisually no problem. Embodiments of the simplifying methods will bedescribed below.

The first simplifying method is a method wherein only important data isselected from the basic code string S11 (coding data). As mentionedabove, the basic code string S11 comprises signals of variouscharacteristics, which include mode data, a motion vector and apredictive residual signal. The code-string simplifier 28 selects onlymore important signals from the signals forming the basic code stringS11 to output the selected signals as the simplified code string S18,and the code-string delay circuit 22 delays the simplified code stringS18 to output the additional code string S12.

For example, an example of a typical code string as shown in FIG. 8(a)will be considered. As described in FIGS. 1 and 2, in the case of amoving-picture coding and/or decoding system using themotion-compensated adaptive prediction coding, a prediction signal isprepared by the motion compensation in a first step, and a predictiveresidual signal is added to the prediction signal in the next step. Inthis case, since the decoding system can obtain a decoded image signalof a certain level if the signals up to the prediction signals areprepared, it is limited to only the data, by which the prediction signalcan be prepared by the motion compensation, to form the simplified codestring S18, i.e. the additional code string S12. In addition, since theblock of INTRA mode can be expressed by the prediction, signal, the DCcomponent of the block of INTRA mode is added to the additional codestring S12 so as to correspond to the INTRA mode. Thus, the additionalcode string S12 is formed to be synthesized with the basic code stringS11, so that it is possible to effectively enhance the error resilience.

FIGS. 8(b) and 8(c) illustrate proposed methods I and II which use codestrings corresponding to those in the first and second proposed methodsshown in FIGS. 5(b) and 5(c) in the first preferred embodiment. In thefigures, the signs n−1, n and n+1 described at the lower-right of therespective blocks indicate what number of frame the data of the blockbelongs to.

The second simplifying method will be described below. Theaforementioned first simplifying method is effective when coding at alow bit rate. However, in the case of a high bit rate, if only theprediction signal is reproduced, it is often greatly different from theoriginal image. Therefore, it is also required to incorporate thepredictive residual signal of a certain extent into the additional codestring S12. In this case, it is possible to resstring the increase ofthe code amount by selecting only blocks having predictive residualsignals of high level or by selecting and outputting components near thelow region of the DCT coefficient obtained by the discrete cosinetransform, i.e. components corresponding to the coefficient expressed bythe slanting lines in FIG. 9, which indicate the DCT coefficient.

In the second simplifying method as set forth above, the code amount maynot be sufficiently reduced to a target amount by simply selecting thesignal. As a method for dealing with such a case, the third simplifyingmethod will be described. Although the simplified code string S18 isdirectly outputted after the signal is selected in the aforementionedmethods, the simplified code string S18 is outputted after the accuracyis lowered in the third simplifying method. For example, the motionvector of a half picture element (pixel) unit is requantized into amotion vector of an integral pixel unit which is outputted as thesimplified code string S18.

In addition, the predictive residual signal outputted as the simplifiedcode string S18 is requantized using a greater quantization width than atypical quantization width, so that it is possible to decrease the codeamount in comparison with the first and second simplifying methods. Theaccuracy of requantization is good when the quantization is performedusing a new great quantization width obtained by returning to thediscrete-cosine-transformed coefficient level and the motioncompensation. However, since such processing takes a lot of time, amethod for further quantizing by reducing the quantized value to halfand so forth may be used.

The second preferred embodiment of an image data decoding systemaccording to the present invention will be described below. FIG. 10 is ablack diagram of the second preferred embodiment of an image datadecoding system according to the present invention, which corresponds tothe image data coding system shown in FIG. 7. Since the basic operationsof the respective sections are the same as those of the image datadecoding system in the first preferred embodiment shown in FIG. 6, onlythe different points will be described below.

The decoding system in this preferred embodiment is substantially thesame as that in the first preferred embodiment, except that a firstswitch 31 is changed over to an additional code string S12 by means of aswitch control signal S17 inputted from an error detector 27 on thebasis of a decoded state indicative signal S14 inputted from a decoder26 when an error occurs, and thereafter, the additional code string S12is temporally inputted to an additional code-string interpolator 32, notdirectly inputted to the decoder 26. The additional code-stringinterpolator 32 adds lack data to the additional code string S12 andrestores data deformed by requantization and so forth so that theadditional code string S12 simplified by the aforementioned firstthrough third simplifying methods can be decoded by the decoder 26.

If the image data coding system has the code-string construction whichpermits the direct input into the decoder 32, it is not required toprovide the additional code-string interpolator 32, so that the decodingcan be performed by the same image data decoding system as that in thefirst preferred embodiment shown in FIG. 6. For example, when thepredictive residual signal is omitted, the mode data may be rewritten tobe preset to a mode having no prediction residual error to form anadditional code string.

In addition, when the additional code string S12 is simplified, if thebasic code string is replaced by only the additional code string in theimage data decoding system, the quality of the decoded image isdeteriorated by the simplified parts in comparison with the quality ofthe decoded image when no error occurs. Therefore, similar to the imagedata decoding system in the first preferred embodiment, when the basiccode string is inputted to the decoder 26 via the second switch 33 to bedecoded, the correctly decoded signal is directly outputted as thedecoded image signal S16, and the signal in which the additional codestring is decoded with respect to only the lack data due to error isoutputted as the decoded image signal S16. Thus, it is possible toresstring the influence of the lack data by simplifying the additionalcode string.

FIG. 11 is a block diagram of the third preferred embodiment of an imagedata coding system according to the present invention. The feature ofthis preferred embodiment is that a synchronizing signal adder 35 isnewly added. In this embodiment, although the synchronizing signal adder35 is added to the image data coding system in the first preferredembodiment shown in FIG. 4, it may be added to the system in the secondpreferred embodiment shown in FIG. 7.

This system is different from the first and second preferred embodimentsat the point that when an additional code string S12 is outputtedthrough a code-string delay circuit 22, a synchronizing signal is addedto the additional code string S12 in the synchronizing signal adder 35.The advantage of this system is that since one synchronizing interval isformed by the additional code string S12 by adding the synchronizingsignal, the additional code string S12 is independent of a basic codestring S11, and errors occurring in other synchronizing intervals haveno influence upon the additional code string S12. In addition, since theerror occurring in the additional code string S12 is closed therein, ithas no influence upon the other synchronizing intervals. Therefore,there is a smaller influence of error than the first and secondpreferred embodiments, so that it is possible to further enhance theerror resilience.

In addition, when the additional code string is divided by the imagedata decoding system, the processing can be performed for each ofsynchronizing intervals, so that the division can be easily performed.However, it is required to use an additional data for discriminatingwhether the read data in a synchronizing interval corresponds to a basiccode string or an additional code string. As such discriminatingmethods, two methods will be described below.

A first discriminating method is a method for discriminating whether itcorresponds to a basic code string or an additional code string by meansof synchronizing signals. That is, it is determined by preparingdifferent synchronizing signals for the basic code string and Sheadditional code string to put each synchronizing signal to its properuse. A second discriminating method is a method for using the samesynchronizing signal for a basic code string and an additional codestring to discriminate whether it corresponds to the basic code stringor the additional code string on the basis of the subsequent headerinformation.

Comparing the first and second discriminating methods, although it isbetter to prepare two different synchronizing signals as the firstdiscriminating method from the standpoint of efficiency of the coding,it is required to select a synchronizing signal which is quite differentfrom those of the other codes. Thus, it is possible to more easilyrealize the second discriminating method which does not newly prepareanother synchronizing signal and which has one synchronizing signal toperform the discrimination by the subsequent header information.

However, if it is interpreted that the header information is alsoincluded in the synchronizing signal, it is consider that the seconddiscriminating method performs the discrimination by a longsynchronizing signal, so that the first and second discriminatingmethods are the same. Therefore, in FIG. 12 which illustrates theconstruction of code strings in this preferred embodiment, only the caseusing two synchronizing signals is shown. In FIG. 12, the signs n andn+1 described at the lower-right of the respective blocks indicate whatnumber of frame the data of the block belongs to. That is, FIG. 12(b)illustrates code strings in a third proposed methods, and FIG. 12(c)illustrates code strings in proposed method II.

The third preferred embodiment of an image data decoding systemaccording to the present invention will be described below. FIG. 13 is ablock diagram of the third preferred embodiment of an image datadecoding system according to the present invention, which corresponds tothe image data coding system shown in FIG. 11. This system is differentfrom the image data decoding systems in the first and second preferredembodiments shown in FIGS. 4 and 7 at the point that an additionalcode-string divider 24 for dividing an input code string 510 into abasic code string S11 and an additional code string S12 for outputting,includes a synchronizing signal discriminator 36 for discriminatingwhether the input code string S10 is the basic code string 511 or theadditional code string S12, and controls a switch 37 for dividing theinput code string S10 into the basic code string S11 and the additionalcode string S12 for outputting on the basis of the discriminatedresults.

Other constructions, i.e. a switch 25′ for selectively inputting thebasic code string S11 or the additional code siring S12 to a decoder 26,the decoder 26 and an error detector 27 are the same as those of theimage data decoding system in the first and second preferredembodiments.

In addition, in this preferred embodiment, it is possible to enhance thequality of a decoded image by using the correctly decoded parts of thebasic code string and by replacing only parts, which have not beendecoded due to error, with data obtained by decoding the additional codestring, similar to the image data decoding system in the secondpreferred embodiment.

Moreover, in this preferred embodiment, it is possible to realize astronger error resilience by inserting a synchronizing signal before apredictive residual signal in the basic code string.

FIG. 14 is a view illustrating the construction of code stringsaccording to this system. In order to avoid waste of the code amount,the synchronizing interval formed by a first synchronizing signalconsists of the minimum amount of data which can prepare a predictionimage by the motion compensation, and a mode data, a residual signal andso forth which relate to a residual signal are incorporated into thesynchronizing interval formed by the subsequent second synchronizingsignal. In addition, as mentioned above, the contents corresponding tothe additional code string are incorporated into the synchronizinginterval formed by a third synchronizing signal.

As described in a forth proposed method in FIG. 14, when the decoding isperformed, if an error occurs in the first synchronizing interval, adecoded image signal is prepared by preparing a prediction image by theadditional code string in the third synchronizing interval and by addingthereto a residual signal in the second synchronizing interval. In thiscase, if the information relating to the preparation of the predictionsignal on the basis of the additional code string is the same as that inthe first synchronizing interval, it is possible to perform thecompletely correct decoding. In a case where an error occurs in thesecond synchronizing interval, a decoded image signal is prepared bypreparing a prediction image on the basis of the information in thefirst synchronizing interval and by combining the image correctlydecoded by the information in the second synchronizing interval, withthe information relating to the residual signal contained in theadditional code string in the third synchronizing interval. In a casewhere an error occurs in the third synchronizing interval, since thedata in the first and second synchronizing intervals may be directlydecoded, so that it is possible to perform the completely correctdecoding (see FIGS. 15 through 17).

Thus, in a case where an error occurs in the basic code string, themethod for simply switching the basic code string to the additional codestring is not used, and the decoding is performed by using the partswhich have been correctly decoded in the basic code and by addingthereto the contents of the additional code string, so that it ispossible to practically use the maximum amount of data which have beendecoded.

As a forth preferred embodiment, an embodiment of a code-stringsimplifier 28 described in the second preferred embodiment will bedescribed below.

FIG. 18 is a block diagram of this code-string simplifier. In thispreferred embodiment, an input code string S11 inputted from an encoder(not shown) includes a DCT coefficient and a motion vector data whichhave been quantized before being variable-length coded byvariable-length encoders 7 and 9 in the moving-picture coding systemshown in FIG. 1 for example. This input code string S11 is inputted toan important data selector 29 wherein only relatively important data S19are selected to be inputted to a code-string transformer 30. Thecode-string transformer 30 transforms the input important data S20 intoanother code string S18 (e.g. a code string of variable-length codes)using a code table (e.g. a variable-length code table). The code tabledescribes the relationship between coded object values and code words(e.g. variable-length code words) in a memory. In this embodiment, whenthe important data S20 is inputted as a coded object value, a code wordcorresponding thereto is outputted as the code string S18.

For example, when the encoder is a moving-picture coding system usingthe motion compensation and the predictive residual coding as shown inFIG. 1, the important data selector 29 selects, as the important data,only the header portion containing the data relating to the coding andthe motion vector data since the motion vector data is more importantthan the quantized DCT coefficient which is the predictive residualsignal. In this case, since there is no motion vector when the encoderis in the intraframe coding mode, the important data selector 29 selectsno data. Therefore, in the intraframe mode, a DC component of the DCTcoefficient is selected in place of the motion vector data. Thus, it ispossible to select the important data in both of the interframe andintraframe modes.

Alternatively, in the important data selector 29, components near thelow region of the DCT coefficient of the predictive residual signal maybe selected as the important data, or the data obtained by thinning outthe motion vector data may be selected as the important data, withoutselecting all the motion vector data. For example, the motion vectorsobtained per 8 pixels×8 pixels are transformed into motion vectors per16 pixels×16 pixels, which are selected as the important data.

The code-string transformer 30 transforms the important data S20 into acode string using a code table such as a variable-length code table asmentioned above. The code table in the code-string transformer 30, i.e.the code table for producing an additional code string, may be differentfrom or the same as the code table for producing the basic code string.Since each of such code tables has its merits and demerits, each tablemay be put to its proper use in accordance with the purpose.

First, the case that the code-string transformer 30 uses an exclusivecode table different from the code table for basic codes strings will bedescribed.

When a basic code string is produced, a code table optimally prepared inview of all the data including the data other than the important data isusually used. Therefore, in a case where the code-string transformer 30transforms only the important data into a code string, if the code tablefor basic code strings is directly used, there are redundant portions.Accordingly, in a case where the coding rate of a channel is regarded asimportant, the code-string transform of the important data S20 iscarried out using a code table suitable for additional code strings inthe code-string transformer 30 in addition to the code table for basiccode strings. Thus, it is possible to efficiently perform the coding.

Next, the case that the code-string transformer 30 uses the same codetable as the code table for basic code strings will be described.

Thus, if the code table for producing basic code strings and the codetable for producing additional code strings are commonly used, since itis not required to especially prepare an additional decoder for decodingadditional code strings as will be described later, it is possible tomaintain the circuit size of the decoder so as to be the same as thoseof conventional decoders. In order to realize this, for example, the DCTcoefficient of the predictive residual signal is not transmitted andonly the motion vector data is selected as the important data, and whenit is transmitted as an additional code string through the code-stringtransformer 30 a mode data indicating that there is a predictiveresidual signal is transformed into a mode data indicating that there isno predictive residual signal, by means of the basic code string toproduce an additional code string. Thus, it is possible to produce anadditional code string using the same code table as that of the basiccode string.

FIG. 19 is a block diagram of the fifth preferred embodiment of an imagedata decoding system according to the present invention. It isdiscriminated in a code-string discriminator 36 whether an input codestring S21 is a basic code string or an additional code string. When itis discriminated that it is an additional code string, it isdiscriminated whether it is an additional code string corresponding tothe previously decoded basic code string. On the basis of thesediscriminated results, a code-string switch 37 is changed over. Thus,when the input code string S21 is a basic code string, it is inputted toa basic code-string decoder 38, and when the input code string S21 is anadditional code string, the code string S21 is inputted to an additionalcode-string decoder 39.

The basic code-string decoder 38 and the additional code-string decoder39 are designed to output decoded state data S25 and S6 independently ofthe decoded values S23 and S24, respectively. The decoded state data S25and S26 are data indicating whether the decoding has been correctlyperformed. For example, the data S25 and S26 are error detection dataobtained by the basic code-string decoder 38 and the additionalcode-string decoder 39.

A decoded value selector 40 selects a decoded value estimated to becorrect, from the decoded value S23 of the basic code-string decoder 38and the decoded value S24 of the additional code-string decoder 39, onthe basis of the discriminated results S22 of the code-stringdiscriminator 36, the decoded state data S25 of the basic code-stringdecoder 38, and the decoded state data S26 of the additional code-stringdecoder 39, and controls a decoded-value switch 41 so that the selecteddecoded-value is outputted as an output coding value S28. That is, thedecoded-value switch 41 selectively outputs the decoded value S23 or S24of the basic code string or the additional code string using adecoded-value switch control signal S27 outputted from the decoded valueselector 40.

According to this preferred embodiment, it is possible to output acorrect decoded value among the decoded values S23 and S24 outputtedfrom the basic code-string decoder 38 and the additional code-stringdecoder 39, using the decoded state data S25 and S26, such as errordata, outputted from the basic code-string decoder 38 and the additionalcode-string decoder 39. This preferred embodiment is particularlyeffective in an image data decoding system in the case of (1) of thefifth preferred embodiment, i.e. in a case where the basic code stringand the additional code string obtained by an image data coding systemare coded by different code tables.

FIG. 20 is a block diagram of the sixth preferred embodiment of an imagedata decoding system according to the present invention. It isdiscriminated in a code-string discriminator 36 whether an input codestring S31 is a basic code string or an additional code string. When itis discriminated that the input code string S31, is an additional codestring, it is discriminated that the input code string S31 is anadditional code string corresponding to the previously decoded basiccode string. In addition, the input code string S31 is decoded by acode-string decoder 42. Moreover, when it is a basic code string, adecoded value S34 is stored in a decoded-value storage 43. Thecode-string decoder 42 outputs a decoded state data S33 such as errordata indicating whether the decoding has been correctly performed,independently of the decoded value S34.

The decoded-value selector 40 selects a decoded value estimated to becorrect, from the decoded value of the basic code string and the decodedvalue S34 of the additional code string, on the basis of thediscriminated result S32 of the code-string discriminator 36 and thedecoded state data S33 outputted from the code-string decoder 42, andcontrols a decoded-value switch 44 so that the selected decoded-value isoutputted as an output coding value S37. That is, the decoded-valueswitch 44 selectively outputs any one of the decoded value S35 of thebasic code string outputted from the decoded-value storage 43 and thedecoded value S34 of the additional code string outputted from thecode-string decoder 42.

According to this preferred embodiment, it is possible to realize adecoder having substantially the same circuit scale as those ofconventional systems, since the basic code string and the additionalcode string can be decoded by means of the same code-string decoder 42.This preferred embodimeat is particularly effective in an image datadecoding system in the case of (2) in the fourth preferred embodiment,i.e. in a case where the basic code string and the additional codestring obtained by an image data coding system have been coded by thesame code table.

As a seventh preferred embodiment of the present invention, adiscriminating algorithm in the code-string discriminator 36 used in thefifth and sixth preferred embodiments will be described below.

FIG. 21 illustrates an example of a basic construction of a code string.At the head of the code string, a synchronizing signal (PSC) isarranged. Subsequently, an ID for discriminating whether an input codestring is a basic code string or an additional code string is arranged,and then, a data TR representative of a time position of the code stringis arranged. Finally, a coded data DATA is arranged.

The code-string discriminator discriminates whether an input code stringis a basic code string or an additional code string on the basis of theID. When it is discriminated by the ID that it is an additional codestring, it is also discriminated whether the code string has the sametime position as that of the basic code string decoded at the last timeby the TR. Thus, it is possible to discriminate the basic code stringand the additional code string corresponding thereto.

However, according to this method, when an error occurs in a channel,malfunction may occurs due to erroneous correspondence for the basiccode string and the additional code string. For example, there will beconsidered the case that from the original code string expressed by theuppermost stage in FIG. 22, only basic code string 1 and additional codestring 2 are decoded as shown in FIG. 22(a), and a time position data TRof the additional code string is erroneously coincide with a TR of thebasic code string 1. In this case, one image must be formed by the basiccode string 1 to be outputted, and thereafter, one image must be formedby only the additional code string to be outputted. However, inpractice, the parts correctly decoded by the basic code string 1 and theadditional code string 2 are combined to be outputted as one image.

In addition, as shown in FIG. 22(b), there will be considered the casethat it is not discriminated that the basic code string 2 corresponds tothe additional code string 2 due to error in the TR of the basic codestring 2. In this case, although the basic code string and theadditional code string must be combined to form one image, two differentimages are formed.

In order to avoid such disadvantage, the relationship between the basiccode string and the additional code string is discriminated, forexample, in accordance with an algorithm shown in FIG. 23. It is assumedherein that the time position date TR of the basic code string is TR1,the TR of the additional code string is TR2, and the TR decoded at thelast time is Pre_TR. In addition, when it has been coded by a fixedframe rate, the differential value Skip_Time between the Pre_TR and thecorrect TR1 and TR2 is also known.

In the algorithm of FIG. 23, it is first discriminated at step S11whether TR1 is equal to TR2. When TR1 is equal to TR2, it isdiscriminated that the decoded additional code string corresponds to thebasic code string decoded immediately before. On the other hand, whenTR1 is not equal to TR2, it is discriminated at Step S12 whether thedifferential value Skip_Time is known. When it is known, the valueobtained by adding the Skip_Time to the Pre_TR is compared with TR2 atstep S13. When these values are equal to each other, it is discriminatedthat TR1 of the basic code string therebetween is incorrect. Then, atstep S14, TR1 is modified to be TR2, and it is discriminated that thedecoded additional code string corresponds to the basic code stringdecoded immediately before. This is shown in FIG. 24.

When it is discriminated at step S12 that the Skip_Time is not known, orwhen it is discriminated at step S13 that the value derived by addingthe Skip_Time to the Pre_TR is not equal to TR2, it is discriminatedthat the decoded additional code string does not corresponds to thebasic code string decoded immediately before.

Although the algorithm of FIG. 23 can cope with the case that an erroroccurs in the time position data TR of the basic code string, it can notcope with other errors. Therefore, when it is required to consider errorresilience so as to be able to cope with other errors, the relationshipbetween the basic code string and the additional code string inaccordance with an algorithm shown in FIG. 25. It is assumed herein thatSingle_Error_Check (A, B) is a function for discriminating whether thevalue derived by adding 1-bit error to A is equal to B.

That is, it is first discriminated at step S21 whether TR1 is equal toTR2. When TR1 is equal to TR2, it is discriminated that the code string1 is the basic code string of the code string 2. On the other hand, whenTR1 is not equal to TR2, it is discriminated at step S22 whether thevalue derived by adding 1-bit error to TR1 is equal to TR2. When theyare equal to each other, it is discriminated that the code string 1 isthe basic code string of the code string 2, and when they are not equalto each other, it is discriminated at step S23 whether the differentialvalue Skip_Time is known. When it is known, it is discriminated at stepS24 whether the value derived by adding 1-bit error to the sum of thePre_TR and the Skip_Time is equal to TR2. When they are equal to eachother, it is discriminated that TR1 of the basic code string isincorrect, and TR1 is modified to be TR2 at step S25. Then, it isdiscriminated that the code string 1 is the basic code string of thecode string 2.

When it is discriminated at step S23 that the Skip_Time is not known; orwhen it is discriminated at step S24 that the value derived by adding1-bit error to the sum of the Pre_TR and the Skip_Time is not equal toTR2, it is discriminated that the code string 1 is not the basic codestring of the code string 2.

In accordance with such an algorithm, it is possible to correctlydiscriminate even if 1-bit error is inserted into TR. This is shown inFIG. 26. Furthermore, if it is desired to discriminate a greater errorthan 1 bit, this function may be changed so as to correspond to theallowable error number.

As an eight preferred embodiment, an embodiment of the decoded-valueselector 40 used in the fifth and sixth preferred embodiments will bedescribed below. FIGS. 27 and 28 illustrate examples of selectingmethods in a decoded-value selector in this preferred embodiment.

In the decoded-value selecting method as shown in FIG. 27, error data oneach of small regions of images of a basic code string and an additionalcode string are received from the basic code-string decoder 38 and theadditional code-string decoder 39 shown in FIG. 19 or from thecode-string decoder 42 shown in FIG. 20. These error data are includedin the decoded-state data S25 and S26 in the case of FIG. 19 or in thedecoded-state data S33 in the case of FIG. 20.

On the basis of these error data and the results discriminated by thecode-string discriminator 36 shown in FIG. 19 or 20, it is determinedwhether the decoded value of the basic code string or the additionalcode string is used for each of the small regions of the image. FIG. 27shows there is an error in the region expressed by the sign X. Since anadditional code string is a code string obtained by simplifying a basiccode string, the decoded value of the basic code string is usuallyselected in the region correctly decoded in the basic code string. Inthe region wherein the basic code string is incorrect and the additionalcode string is correctly decoded, the decoded value of the additionalcode string is selected. In the region wherein errors exist in both ofthe basic code string and the additional code string, a mode in whichthe last frame is directly used is selected (not coded).

Thus, when the decoded values of the basic code string and theadditional code string are selectively used for each of the smallregions, it is possible to decode more regions than when only thedecoded value of any one of the basic code string and the additionalcode string is used. However, in the case of a communication state of ahigh error rate, regions decoded without fining out an error may exist.In such a case, decoded values is not selected for each of the regions,so that it is possible to use decoded values for each of completelydecoded frames.

The decoded-value selecting method shown in FIG. 28 will be described.In the case of the decoded-value selecting method shown in FIG. 27, theerror which has not been found when decoding the basic code string isdirectly output as an incorrect decoded value. On the other hand, in thedecoded-value selecting method shown in FIG. 28, a decoded value isselected using the decoding data, in addition to the error data when thedecoding is performed. The decoding data includes a mode datarepresentative of a coding mode such as an intraframe coding and aninterframe coding.

The matching of the decoding data is examined for each of the smallregions of the basic code string and the additional code string. Forexample, when the mode data varies in a certain small region, it isdetermined that an error occurs in the small region. Thus, it ispossible to decrease the probability of oversight of errors. Inaddition, if the reliability of an additional code string is enhancedusing an error correcting code and so forth in the additional codestring, it is possible to use a method for selecting the data on theadditional code string for the small region in which the mode datavaries. Moreover, for example, if an INTRA mode number is added to anadditional code string, it is possible to enhance the detection accuracyof an error caused when a mode is erroneously changed to another mode.

FIG. 29 is a block diagram illustrating a main portion of the ninthpreferred embodiment of an image data coding system according to thepresent invention, particularly illustrating an encoder 46, asimplification controller 47 and a code-string simplifier 40. Thecode-string simplifier 48 is basically the same as the code-stringsimplifier 28 shown in FIG. 7.

An input image signal S41 is coded by the encoder 46 on the basis of acoding data S43 outputted from the encoder 46 independently of a codestring S42, the simplification controller 47 determines a simplifyingmethod in the code-string simplifier 48 by a simplifying method controlsignal. In accordance with the determined simplifying method, thecode-string simplifier 48 simplifies the code string S42 outputted fromthe encoder 46, and outputs a simplified code string S45.

The coding data S43 is data representative of, for example, (a) a codeamount produced by the encoder 46, (b) the magnitude of a motion vectorused for the encoder 46, (c) the number of intraframe coding regions and(d) the magnitude of a predictive residual signal. All of (b) through(d) are data on error resilience since the influence of error increasesas their values increase. The simplification controller 47 controls thecode-string simplifier 48 on the basis of the coding data S43, i.e. thedata on the code amount of a code string and the data on the errorresilience of the code string.

Specifically, in a case where there is a room in the code amount, theDCT coefficient of a predictive residual signal is also selected as theimportant data in addition to the motion vector. Alternatively, in aregion having a great predictive residual signal, the DCT coefficient ofa predictive residual signal may be selected as the important data. Inaddition, in a case where the DCT coefficient of a predictive residualsignal is selected as the important data, it is effective means toreduce the code string by quantizing the predictive residual signalusing a greater quantization width than the quantization width used forcoding the basic code string in the encoder 46, without using the samepredictive residual signal as that in the basic code string. Moreover,the processing for selecting more predictive residual signals of INTRAmode, which has a great influence when an error occurs, than thepredictive residual signals of INTRA mode may be carried out. Inaddition, in a case where there is no room in the code string, it mayswitch whether the produced additional code string is outputted.

According to the ninth preferred embodiment, it is possible to adjustthe produced code amount by simplifying the frame unit and so forth inaccordance with the state of the coding, or to protect intensively onlya part wherein a great error may be caused.

As mentioned above, while the preferred embodiments of the presentinvention have been described, the present invention should not belimited to the method for combining a basic code string and anadditional code string as described in the preferred embodiments, but itmay be applied to various combining methods. In addition, while thepreferred embodiments have been applied to a moving-picture coding, thepresent invention should not be limited to the moving-picture coding,but it may be applied to a still-picture coding. Moreover, the presentinvention should not be limited to an image coding, but it may beapplied to other codings such as an audio coding.

Referring to FIG. 30, as an example to which the present invention isapplied, the preferred embodiment of a moving-picture transmissionsystem 50 to which an image data coding and/or decoding system of thepresent invention is applied, will be described below.

A moving picture signal inputted from a camera 52 provided on a personalcomputer (PC) 51 is coded by an image data coding system build in the PC51. After a coded data outputted from this image data coding system ismultiplexed with other audio and data information, it is transmitted viaa radio communication by means of a radio transmitter-receiver 53, andreceived by another radio transmitter-receiver 54. The signal receivedby the radio transmitter-receiver 54 is divided into coded data of themoving picture signal and information on audio and data. Among them, thecoded data on the moving picture signal is decoded by an image datadecoding system built in a workstation (EWS) 55, and displayed on theEWS S5.

On the other hand, a moving picture signal inputted from a camera 56provided on the EWS 55 is coded using an image data coding system builtin the EWS, in the same manner as that set forth above. After the codeddata of the moving picture signal is multiplexed with other audio anddata information, it is transmitted via a radio communication by meansof the radio transmitter-receiver 54, and received by the radiotransmitter-receiver 53. The signal received by the radiotransmitter-receiver 53 is divided into coded data of the moving picturesignal and information on audio and data. Among them, the coded data ofthe moving picture signal is decoded by an image data decoding systembuild in the PC 51, and displayed on the PC 51.

FIGS. 31(a) and 31(b) are block diagrams schematically illustrating animage data coding system 60 and an image data decoding system 70 builtin the PC 51 and the EWS 55 of FIG. 30, respectively.

The image data coding system shown in FIG. 31(a) includes an informationsource coding section 62 which receives an image signal from an imageinput section 61 such as a camera and which has an error resilienceprocessing section 63, and a channel coding section 64. The informationsource coding section 62 performs the discrete-cosine transform (DCT) ofa predictive residual signal, the quantization of the produced DCTcoefficient and so forth. The channel coding section 64 performs thevariable-length coding, the error detection on the coded data, the errorcorrection coding and so forth. The coded data outputted from thechannel coding section 64 is transmitted to a radio transmitter-receiver65 for a radio communication.

On the other hand, the image data decoding system 70 shown in FIG. 31(b)includes a channel decoding section 72 for inputting the coded datareceived by a radio transmitter-receiver 71 to perform the inverseprocessing of that performed in the channel coding section 64, and aninformation source decoding section 73 which receives a signal outputtedfrom the channel decoding section 72 to perform the inverse processingof that performed by the information source coding section 62 and whichhas an error resilience processing section 74. The image decoded by theinformation source decoding section 73 is outputted by an image outputsection 75 such as a display.

1. An image data signal for transmitting encoded image information in anoutput code string, said output code string comprising: an encoded imagestream including a code string composed of a synchronization code; abasic code string obtained by coding an input image signal; adiscrimination code which is different from the synchronization code;and an additional code string including at least a part of said basiccode string.
 2. An image data signal according to claim 1, wherein theoutput code string is embodied in a signal transmitted betweencomputers.
 3. An image data signal according to claim 1, wherein theoutput code string is embodied in a radio frequency signal transmittedbetween computers.
 4. An image data signal for storing encoded imageinformation as an output code string in a computer readable medium, saidoutput code string comprising: an encoded image stream including a codestring composed of a synchronization code; a basic code string obtainedby coding an input image signal; a discrimination code which isdifferent from the synchronization code; and an additional code stringincluding at least a part of said basic code string.
 5. An image datasignal according to claim 4, wherein the output code string is embodiedin a signal transmitted between computers.
 6. An image data signalaccording to claim 4, wherein the output code string is embodied in aradio frequency signal transmitted between computers.
 7. An image datasignal for transmitting encoded image information in an output codestring, said output code string comprising: an encoded image streamincluding a code string composed of a first synchronization code; abasic code string obtained by coding an input image signal; a secondsynchronization; and an additional code string including at least a partof said basic code string.
 8. An image data signal according to claim 7,wherein the output code string is embodied in a signal transmittedbetween computers.
 9. An image data signal according to claim 7, whereinthe output code string is embodied in a radio frequency signaltransmitted between computers.
 10. An image data signal for storingencoded image information as an output code string in a computerreadable medium, said output code string comprising: an encoded imagestream including a code string composed of a first synchronization code;a basic code string obtained by coding an input image signal; a secondsynchronization; and an additional code string including at least a partof said basic code string.
 11. An image data signal according to claim10, wherein the output code string is embodied in a signal transmittedbetween computers.
 12. An image data signal according to claim 10,wherein the output code string is embodied in a radio frequency signaltransmitted between computers.
 13. A video signal encoding methodcomprising: dividing frames, which compose a video signal, into aplurality of blocks; generating first encoded data, which includes firstencoded blocks obtained by encoding the plurality of blocks; generatingsecond encoded data, which includes second encoded blocks obtained byencoding the plurality of blocks; and combining the first encoded dataand the second encoded data so as to output combined encoded data,wherein the combining includes locating the second encoded data behindthe first encoded data in the combined encoded data.